1. Field of the Invention
This invention relates to improvements in dredges.
2. Description of the Prior Art
A well-known type of dredge has a hull with a main section from which two parallel arms extend forwards, a bucket-wheel carrier, having a driven rotary bucket wheel at its front, being located between these arms and hinged at its rear so it can be lowered to working depth, or raised, by means of a cable passed through a sheave block on a gantry straddling the two forwardly extending arms and a further sheave block on the front of the bucket wheel carrier. At the stern of the dredge are two vertically slidable spuds, each of which can be released to drop and drive into the sea bed, one of these spuds being mounted in a carriage longitudinally slidable on the hull, and when this spud has been driven into the sea bed the dredge may be advanced relative to this spud and its carriage, the second spud then being released and driven into the sea bed, after which the first spud is raised and its carriage is returned forwardly on the hull. The spud which at any time is driven into the sea bed serves as a pivot about which the dredge and its bucket wheel can be slewed. For slewing the dredge, a pair of anchors are dropped to both sides of the front of the dredge, the anchors being lowered from booms on the dredge, cables from the anchors being carried through slewing sheave blocks on the front of the bucket wheel section, one of these cables being tensioned as the other is slackened to slew the dredge.
The bucket wheel is driven, through a gearbox, by a hydraulic motor at the front of the bucket wheel section, the hydraulic motor being operated by an engine-driven hydraulic pump on the dredge. The material being dredged is pumped through a conduit carried along the bucket wheel carrier and to the stern of the dredge, from which it is conveyed to the shore by a pontoon-supported conduit.
Although a dredge commonly works at fairly shallow depths, there are many occasions when dredging at greater depths is required. When the bucket wheel carrier is lowered for dredging at these greater depths, there is a likelihood of the failure, after a fairly short time, of the seals at the bucket wheel assembly and of the seals of the submerged sheave blocks of the bucket wheel carrier, that is to say the sheave blocks of the lifting cable and sheave blocks of the slewing cables. Any such failure is likely to result in very costly delays in the operation of the dredge, and the laborious and expensive replacement of the affected apparatus, which may be extensively damaged by the ingress of the highly abrasive material which is suspended in high concentration in the water during the dredging operations.
The present invention has been devised with the general object of providing simple yet effective means for very greatly reducing the likelihood of such seal failures occurring.